Me and a friend of mine was having a debate about this subject. I think they would if they was walking on the carpet barefooted. He thinks they wouldn't notice.
I think you can tell if theres a residue or notI never really believed fiber rinse left carpet soft. But was hearing from customers about how soft their carpet felt in their feet after cleaning. Now i dont know if they would say the same if i had used formula 90. Just think they were used to carpet loaded with soil. And fibers were all clumped together. But hey maybe it does. I know form 90 makes carpet crunchy or stiff. But after vacuuming once its back to normal. Kinda like line drying a pair of jeans. They are solid as a rock after line drying. But after a few minutes of wearing them. They are back to normal.